Centrifuge drum with discharge openings

ABSTRACT

A drum for centrifuges processing substances of relatively high viscosity. The drum has a peripheral wall concentric with its axis of rotation and opposite axial end walls. Outlets are provided in the region of the opposite axial end walls. A plurality of outlet openings are provided in the peripheral wall and each of these has the configuration of a geometric ellipse with the longer axis of the ellipse being normal to the axis of rotation of the drum. A method of making such a drum is disclosed also.

United States Patent Pause 1 May 16,1972

[ CENTRIFUGE DRUM WITH DISCHARGE OPENINGS [72] Inventor: Kurt Pause,Zedemstrasse l3, Grevenbroich, Germany [22] Filed: Mar. 27, 1970 [21]Appl. No.: 23,337

[30] Foreign Application Priority Data Feb. 27, 1970 Germany ..P 19 16280.2

[52] US. Cl. ..233/47 R, 210/380 [51] Int. Cl [58] Field of Search..233/1 R, 2, l C, 46, 47 R,

[56] References Cited UNITED STATES PATENTS 955,889 4/1910 Marshall..233/2 2,688,437 9/1954 Monnet ..233/46R FOREIGN PATENTS ORAPPLICATIONS 436,496 10/1935 Great Britain ..233/46 190,91 1 4/1906Germany ..233/2 945,318 7/1956 Germany ..233/2 336,865 10/1930 GreatBritain ..233/2 Pn'mary Examiner-Jordan Franklin AssistantExaminer-George H. Krizmanich Attorney-Michael S. Striker Filed underRule 478 [57] ABSTRACT 5 Claims, 2 Drawing Figures Patented May 16, 19723,662,947

I I Q i y g 1 v. v I;

FIG. 2

INVENTORI Kwz'r PAUSE ATTORNEY CENTRIFUGE DRUM WITH DISCHARGE OPENINGSBACKGROUND OF THE INVENTION The present invention relates to acentrifuge, and more particularly to a drum for a centrifuge. Still moreparticularly the present invention relates to a drum for a centrifugewhich processes at least at times materials of relatively highviscosity, and to a method of making such a drum.

During the periodic operation of a centrifuge the drum is subjected toincreasing loading, that is from start-up the load acting upon the drumincreases from zero to a maximum value. This recurs during eachoperation of the drum and because the recurrence is very frequent, thelife expectancy of the drum must be evaluated with reference to thedynamic behavior of the material from which the drum is made. It istherefore necessary in constructing such a drum to consider alloccurring stresses in terms of the strength and resistancecharacteristics of the material under the influence of such stresses.

Centrifuges are used in the sugar-producing industry for processingso-called filler mass. There are wide differences between the separatingbehavior of filler masses in that sometimes the separated liquid phasemay have a low viscosity whereas at other times it may have a ratherhigh viscosity. If the liquid phase has a lowviscosity it is necessary,in order to assure proper operation of the centrifuge and properseparation, to throttle the escape of the low-viscosity liquid phase forwhich purpose the centrifuge drum is provided with outlet openings onlyin its opposite axial end walls, or in the region thereof. Thisarrangement has the advantage that the outlet openings are arranged inthose regions of the drum where the stresses acting upon the drum are ata minimum. Because of this it is possible to substantially reduce thewall thickness of the center part of the drum. In other words, thelargest portion of the peripheral wall of drums used for separating fromfiller liquid phase of low viscosity, is imperforate. This of coursenecessitates long distances to be'traversed by the liquid phase beforeit can issue from the outlet openings of the drum. However, where theliquid phase is of low viscosity this is of no importance and thus thewall thickness of the circumferential wall of the drum may be selectedin accordance with nominal stresses and the drum can be economicallymanufactured and lightin weight because stress-concentration factors andnotch fatigue strength need not be considered.

However, drums constructed in this manner cannot be used for theprocessing of masses where the liquid or flowable phase is highlyviscous, for instance molasses. Under these circumstances the flow pathsto be traversed by the separated flowable phase are too large or long,so that the separation of the flowable phase will be irregular andoperating difficulties are experienced. The reason for these operatingdifficulties has been found to be the following: Using thin-walledcentrifuge drums of the type which is conventionally employed withfiller masses from, which low-viscosity phase is to be separated, forthe separation of high-viscosity phase, causes outward bulging ordeformation of the circumferential wall of the drum, and an accumulationof separated syrup-that is relatively high-viscosity phase-at the innerside of such bulge. When the drum is braked down, the thus accumulatedsyrup will flow to the lowermost axial endof the drum under theinfluence of centrifugal force and leave the drum through the outletopenings provided in the region of this axial end. However, while thispresents no problem if the syrup has relatively low viscosity, adifficulty arises if the syrup is of relatively high viscosity.Specifically, high viscosity does not have sufficient time during theshort braking period of the drum to flow towards the lower axial end ofthe drum and instead becomes backed up and is drawn back into thealready dry sugar by capillary action, that is its'ejection under theinfluence of centrifugal force during rotation of the centrifuge isreversed as soon as the centrifuge is braked.

A further problem resides-if the phase is highly viscousin the fact thatthe long flow path to be traversed causes irregular ejection of thephase even while the drum rotates. It is thus necessary that there beshort flow paths provided in centrifuge drums in which the flowable massto be separated by centrifuging has relatively high viscosity. In fact,the critical value for the flow paths is between approximately 200 and250 mm.

It is for this reason that materials from which highly viscous flowablephases are to be separated are processed in centrifuge drums which areperforated over the entire axial length of their circumferential wall.However, under these circumstances the wall must be particularly thickbecause of the perforation over the entire axial length. The reason forthis is that the selection of field conditions in a field with drilledcircular holes is limited by the notch-strength influences. lt ispossible to reduce to some extent the notch tension with reference to anindividual opening by careful selection of the bore diameter as relatedto the spacing between the bores within one row of bores incircumferential direction and with reference to the axial distancebetween the rows of bores. However, the notch influence on the maximumtension at the edge of the bore, which is triple the nominal tension incase of the individual bore, can at most be reduced to 2.5 times thenominal tension. It is not sufficient, and in fact it is impossible byincreasing the wall thickness of the drum in such a manner as toproportionately decrease the tension, because owing to the operatingcircumstances involved in a centrifuge drum the mass of thecircumferential wall is self-loading. The inherent or self-loading,expressed in tangential tension, remains constant with reference to thewall thickness of the drum. The considerations in constructing acentrifuge drum must always be such that the material used for the drumwill have a permissible load limit which is far above the load to whichthe drum will be subjected by the presence of its own mass undercentrifugal conditions. Only then is it possible for the drum towithstand additional load resulting from the presence of the material tobe processed.

0n the other hand, the ability to withstand such an additional loaddecreases with increasing wall thickness, related to such wallthickness. Once a certain thickness of the wall is reached, a furtherthickness increase will no longer provide any improvement because theinertial moment of the filled drum becomes so large that the economicfeasibility of the entire centrifuging process becomes questionable.

As suggested before, to assure that highly viscous flowable phaseseparated from the contents of the centrifuge drum will properly beejected from the drum, it is necessary that bores be provided over theentire surface area of the circumferential wall of the drum. Thepresence of such bores, however, produces in the circumferential wallnotch stresses which are significantly higher than the nominal stress sothat heretofore it was necessary to increase the wall thickness of thedrum, thus losing the advantages which are obtained from a small wallthickness.

SUMMARY OF THE INVENTION It is, accordingly, an object of the presentinvention to overcome the aforementioned disadvantages.

More particularly it is an object of the present invention to provide acentrifuge drum which is capable of centrifugally separatinghigh-viscosity flowable phases without difiiculty and without having toforego the advantages of the type of centrifuge drum utilizing acircumferential wall of small thickness.

It is a concomitant object of the present invention to provide also acentrifugal drum wherein the particular flow-path requirements of ahighly viscous flowable phase are taken into account.

A concomitant object of the invention is to provide the aforementionedadvantages in a centrifugal drum of at least 750 mm axial length.

Still another object of the invention is to provide a method of makingsuch a drum.

In pursuance of the above objects, and others which will become apparenthereafter, one feature of the invention resides in the provision, in acentrifuge and particularly in a periodically rotating centrifuge forsubstances which are at least at times of high viscosity, of acombination which, briefly stated, comprises a drum mounted for rotationabout an axis of rotation and having a peripheral wall which isconcentric with this axis of rotation, and further having opposite axialend walls. Outlet means is provided in the region of the opposite axialend walls, and a plurality of outlet openings are provided in theperipheral wall and each have the configuration of a geometric ellipsewith the longer axis of the ellipse extending normal to the axis ofrotation.

With a drum constructed in this manner the flow paths can be selected inaccordance with maximum advantage for highly viscous flowable phase, andthe openings constructed in accordance with the present invention may beneglected in the considerations of the drum construction insofar asstresses acting upon the circumferential wall of the drum are concerned.

According to the invention the configuration of each ellipse is to besuch that its notch effect is smaller than 2 percent so that the tensionincreasing influence is within the usual distribution of materialstrength, filler variations, variations in the number of rotations andthe like. In other words, the presence of such elliptical openings mustnot reduce the strength of the circumferential wall with respect totensions acting upon it. It has been found in this context that asemiaxis ratio in excess of l 5, and preferably on the order of l isparticularly advantageous. A centrifuge constructed in accordance withthe present invention and utilizing elliptical outlet openings whoseconfiguration is based on this ratio, can have a wall thicknesscorresponding to the wall thickness conventionally used for centrifugedrums whose circumferential wall is not perforated.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a somewhat diagrammatic axialsection through a centrifuge drum constructed in accordance with thepresent invention;

FIG. 2 is a diagrammatic illustration of an elliptical outlet openingutilized in the centrifuge drum of FIG. 1 in accordance with the presentinvention, and with the stresses acting upon such opening beingillustrated in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Discussing now the drawing indetail it will be seen that in FIG. 1, I have illustrated a centrifugedrum 1 which is conventional in all particulars except for the provisionof the apertures in its circumferential wall. The circumferential wallis identified with reference numeral la and the opposite axial end wallsare identified with reference numeral lb. The drum is mounted by meansof a hub 3 on a shaft 2 for rotation with the latter about an axisdefined by the elongation of the shaft. Reference numeral 4 identifiesoutlet means provided in the region of the opposite axial end walls 112.

Thus far, the drum shown in FIG. 1 is conventional.

However, because the drum of FIG. 1 is to-be capable of operating undercircumstances where highly viscous flowable phase is to be separatedfrom the drum contents by centrifuging, and to obtain under thesecircumstances the advantages which have been outlined and described asdesirable above, the drum in FIG. I is further provided with a pluralityof outlet openings 5 in its circumferential wall la. These outletopenings are arranged as considered necessary in one or several rows,and in accordance with the desired maximumadvantage flow path which havebeen found necessary for optimum operation of such drum in separation ofhigh-viscosity flowable phases.

In accordance with the present invention the outlet openings 5 each havethe configuration of a geometric ellipse whose longitudinal or majoraxis extends normal to the axis of rotation of the drum 1, which axis ofrotationis coincident with the elongation of the shaft 2. It isnecessary, however, that the configuration of the outlet openings 5 beexactly that of a geometric ellipse, as is clearly shown in FIG. 2. Inthis Figure, I have also illustrated the stresses which act upon thecircumferential wall la during rotation of the centrifuge drum 1, in theregion of the respective outlet openings 5. The arrow 0' ax in FIG. 2identifies the axial stress and the arrow at identifies the tangentialstress, indicating that the axial stress is so small as to benegligible, so that the centrifuge drum 1 need be constructed only withthe expected tangential stresses in mind. The term axial stress ofcourse refers to the axis of the drum 1.

The present invention is based on the realization that twocharacteristic phenomena take place at outlet openings provided in thecircumferential wall of a centrifuge drum. Because of the geometric formchosen for the boundary of the respective outlet opening the surroundingstress is increased to the maximum notch stress. The stress directionacted at the edge of the aperture includes angles with the stressdirection of the surrounding stresses and for this reason stressconditions occur at the edge of the aperture which have several axes andwhich hinder the formations associated with the respective stresses. Itfollows from this that higher stresses act at the edge of the aperturethan would normally occur in the material, and these two influencesbecome evermore' advantageous in an aperture of truly ellipticalconfiguration with stretching of the ellipsis in the tensile directionunder maintenance of its exact geometrical elliptical configuration, andreach an optimum at a semi-axis ratio of l 10.-

It must be emphasized that the configuration of the apertures must be incorrespondence with an exact geometrical ellipse, and that a merely ovalaperture will not provide the results according to the presentinvention. The reason for this is that an oval aperture will not permitdefinitions because an oval aperture is terminated at its opposite endsin semi-circular or substantially semi-circular configuration. Becauseof this the stress-increasing influences which occur in thepresence ofan oval aperture are almost equal to those of a circular aperture. Theyare somewhat more advantageous because the semi-circular curvaturemerges into the elonga tion of the oval aperture, that the absolutelength of the oval is without importance because the notch stresses donot decrease with increasing length of the oval aperture.

It is advantageous, but not necessary, that if the apertures accordingto the present invention are arranged in rows, the distance betweenadjacent rows is at most 250 mm, and that the distance between adjacentapertures of any row is also at most 250 mm.

In accordance with the present invention it is advantageous, also, toprovide the novel drum by first making the drum with an imperforatewall, and by forming the elliptical apertures by electrochemicalmaterial removal. This method of producing the elliptical apertures hasthe advantage that the material of the circumferential drum wall,particularly at the edge of the aperture, does not undergo anymetallurgical changes and remains free of internal tension or stresses.In addition, the configuration of the electrode used for effecting thematerial removal and formation of the apertures 5, remains unchanged sothat the elliptical configuration of the aperture 5 is alwaysreproduceable and the ellipsis will always be geometrically ex act.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in acentrifuge drum, it is not intended to be limited to the details shown,since various modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

I claim:

1. In a centrifuge, particularly a periodically rotating centrifuge forsubstances which are at least at times of high viscosity, incombination, a drum mounted for rotation about an axis of rotation andhaving a peripheral wall which is concentric with said axis of rotationprovided with a smooth inner surface throughout, and opposite axial endwalls; outlet means provided in the region of said opposite axial endwalls; and a plurality of circumferentially distributed outlet openingsprovided in said peripheral wall and each having the configuration of ageometric ellipse with the longer axis of the ellipse extendingcircumferentially of said peripheral wall in a plane which is normal tosaid axis of rotation, the ratio of the major to minor axes of eachellipse being in the range of substantially 5:1 and 10:1.

2. In a centrifuge as defined in claim 1, wherein said openings arearranged in at least one row.

3. In a centrifuge as defined in claim 1, wherein said openings arearranged in at least two rows which are spaced from one another by adistance of at most 250 mm.

4. In a centrifuge as defined in claim 2, wherein the distance betweenadjacent ones of said openings is at most 250 mm.

5. In a centrifuge as defined in claim 1, wherein the said ratio is 5:l.

1. In a centrifuge, particularly a periodically rotating centrifuge forsubstances which are at least at times of high viscosity, incombination, a drum mounted for rotation about an axis of rotation andhaving a peripheral wall which is concentric with said axis of rotationprovided with a smooth inner surface throughout, and opposite axial endwalls; outlet means provided in the region of said opposite axial endwalls; and a plurality of circumferentially distributed outlet openingsprovided in said peripheral wall and each having the configuration of ageometric ellipse with the longer axis of the ellipse extendingcircumferentially of said peripheral wall in a plane which is normal tosaid axis of rotation, the ratio of the major to minor axes of eachellipse being in the range of substantially 5:1 and 10:1.
 2. In acentrifuge as defined in claim 1, wherein said openings are arranged inat least one row.
 3. In a centrifuge as defined in claim 1, wherein saidopenings are arranged in at least two rows which are spaced from oneanother by a distance of at most 250 mm.
 4. In a centrifuge as definedin claim 2, wherein the distance between adjacent ones of said openingsis at most 250 mm.
 5. In a centrifuge as defined in claim 1, wherein thesaid ratio is 5:1.